Internal combustion engines have a fuel supply system for their supply with liquid fuel. Such a fuel supply system comprises typically a fuel tank, a fuel pump, a fuel filter, and an injection system. To reduce the risk of damage of the injection system or the internal combustion engine, respectively, it is required to clean the fuel supplied to the internal combustion engine from contamination carried along with the fuel. Hence, the fuel filter is a component which is relevant for the functional reliability of the internal combustion engine. Such a fuel filter has typically a filter housing which comprises an untreated-side inlet and a treated-side outlet. Furthermore, a filter element is provided, which is arranged in the filter housing and which separates in the filter housing an untreated space communicating with the inlet from a treated space communicating with the outlet. The filter element is a wear part which is replaced in certain maintenance intervals. When replacing the filter element, there is a risk that it is not properly installed in the filter housing. Moreover, there is a risk that the fuel filter is operated, accidentally or knowingly, without filter element. With missing or improper installed filter element, there is the risk that contamination can get unhindered to the injection system or to the internal combustion engine, respectively.